Fighting a fish is a tug-o-war on a tight rope. And like most things, technique plays a big part in the outcome. The trick is to land the fish as quickly as humanly possible. The longer a fish is played the closer it comes to exhaustion. And trout (especially in warm water) can easily die from exhaustion. So retrieving that fish quickly is very important. Here are a few things to keep in mind when playing a fish.

1.Be aware of obstructions in the water the fish my get tangled in.
Boulders, logs, stream side branches, undercut banks. Keep your eyes peeled for anything and expect the fish to dart towards these things as it tries to flee for cover.

2.Be aware of currents in the area..
Fast/heavy currents that either you or the trout can use to take the upper hand.
Slower softer currents or back eddies where you can take the upper hand.

3.Keep the rod high and bent.
When the rod is bent it is "working" to absorb energy. It is helping to keep the line tight (thus the hook secure in the fish) and absorbing energy and pressure that the fish is applying.
Keeping the balance of pressure between slack (the hook can easily shake free) or failure (the hook bends or breaks, the line or knots fail, the rod breaks) requires acute tension on the line.
Whether using the reel and it's drag or hand strips/ finger pressure on the line, keep that line tight!

4.Try to get the fish upstream of you.
Either by carefully leading it up or positioning yourself below the fish when you are below you have the current on your side, and the fish's options and ability to move are all reduced and biased towards you.
Similar to walking a dog or leading a horse, by keeping the rod high and applying pressure you can "steer" or lead the fish. Moving it's head is gong change the direction the fish is headed.

5.Momentum is key.
Trout don't have much for breaks, so when ever you get a fish pointed in the direction you need it to go, apply pressure and maximize big gains of line.
To a large degree you can "fast forward" a fish towards you (especially when you are down stream of the fish) if the currents allow and you get it pointed in your direction.
Watch for these opportunities to really "horse" the fish when it briefly stalls during its fight.

6.Heads up.
This almost reminds me of picking up a cat by the scruff of the neck, when you can get a fish's head up out of the water they often give up momentarily.
When a fish's head is up apply max pressure and practically "skip" it in. (Clearly this works better on small fish that your tippet can easily handle).
This also is often prime time to make your move to land the fish.

7.Element of surprise.
There are scenarios where any fish can be caught off guard and landed almost immediately after being hooked. The key is you need to be prepared for the rare occasions where the fish presents this opportunity.
Try to stay stealthy, calm and still so the fish does not see itself being pulled towards a cluster of thrashing gore-tex screaming like a little girl.